Set parts of a given array vec to zero according to fixed atom constraints. When atoms are (partially) fixed then the relevant components of nvec should be set to zero. Furthermore, the relevent components of the gradient in CG should also be set to zero.

Arguments:

Arguments:

Set parts of a given array vec to zero according to fixed atom constraints. When atoms are (partially) fixed then the relevant components of nvec should be set to zero. Furthermore, the relevent components of the gradient in CG should also be set to zero.